Tuesday, 28 June 2016

Sea Life growing on Floating Walkways in a Coral Sea Marina

The floating walkways in the Cairns Marina in tropical
Australia are a new type of habitat that is not seen in nature. Existing species have colonised but in new
combinations to create what is known as a novel community, a community that
does not occur in nature. This
community features a rich multi-coloured carpet of filter feeders. These photos were taken by lying down on the walkway and holding a a low cost underwater camera in the water with my hand. I would probably modify my technique if gropers were known live in the marina.

A garden of sponges, sea squirts and hydroids

The floating concrete walkways provide a habitat that is different
from natural rocky surfaces in many respects.
This habitat is not exposed to waves or high and low tides as the
walkways rise up and down with the tides and marinas are as protected from
waves as possible. Another difference is
that waters in the marina are deep and there is very little connection between
the floating walkways and substrate on the bottom of the harbour. Indeed sediments fall away from the floating
walkway community. On natural coasts,
sediment from the bottom is constantly being resuspended deposited on hard
surfaces or the hard surfaces are being scoured by sand and waves.

Inlet of a tunicate

Possibly a coral - corals were generally absent

In nature, only fissures between boulders, deep rock pools
on rocky headlands and the vertical sides of fjords have vaguely similar communities as
these locations are protected from wave and sand blasting and from desiccation
at low tide. Forgetting fjords as we
have none in north Queensland, marine life in fissures and rock pools can be
subject to wild swings in temperature and salinity as due to very hot days,
cold nights and intense rainfall events.
In contrast the life attached to walkways enjoys relatively constant
temperatures and salinities. Even when
the same creatures occur in other habitats, they are often larger when they are
attached to walkways.

Hydroids?

Ferny growths are hydroids, a relative of coral

Fish are surprisingly uncommon as perhaps they do not like
the shallow depth of the water and mobile invertebrates such as crabs and
shrimps are also fairly uncommon. Even
macro algae is uncommon which is surprising given that the walkways suspend
their denizens in the bright sunlit surface waters and bath them in nutrient
rich flowing waters. The community is
completely dominated by sessile filter feeders.
As to what species they are, it is a real struggle to find out as very few
people know how to classify these species and resources are hard to find.